ASTM D5766 Tensile Strength (Open Hole)

Standard test method for open-hole tensile strength of polymer matrix composite laminates. ASTM D5766 test is mainly used in the aerospace industry for developing notched design allowable strengths.

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Overview
Scope, Applications, and Benefits
Test Process
Specifications
Instrumentation
Results and Deliverables

Overview

ASTM D5766 – Open-Hole Tensile Strength of Polymer Matrix Composite Laminates is a standard that describes the procedure for measuring the tensile strength of composite laminates with a central hole. The test assesses the influence of stress concentrations around holes, which represent fastener or bolt positions in a structure.

In this test, a flat composite specimen with a machined open hole is loaded uniaxially to failure. The test provides open-hole tensile strength and is critical for structural design, damage tolerance, and performance characterization of mechanically fastened composite structures.

Scope, Applications, and Benefits

Scope

ASTM D5766 covers the determination of the open-hole tensile strength of polymer matrix composite laminates. The method evaluates the tensile behavior of composite materials containing a centrally machined hole to simulate stress concentrations typically found around fasteners or joints.

Applicable to polymer matrix composite laminates.
Uses specimens with a centrally drilled open hole.
Measures open-hole tensile strength.
Assesses stress concentration effects under tensile loading

Applications

Evaluation of mechanically fastened composite joints
Damage tolerance assessment of composite laminates
Material qualification for aerospace structures
Quality control of drilled composite components
Research and development of advanced composites

Benefits

Simulates real fastener hole conditions
Assesses strength reduction due to stress concentration
Supports safe structural design
Provides standardized and comparable data

Test Process

Specimen Preparation

Fabricate flat composite specimens and machine a centrally located hole to the specified diameter and tolerance.

Mounting & Alignment

Install the specimen in the universal testing machine grips, ensuring proper axial alignment to avoid bending.

Tensile Loading

Apply a uniaxial tensile load at the specified rate until failure, recording load and displacement data.

Data Analysis & Reporting

Calculate open-hole tensile strength and document failure mode in accordance with ASTM International.

Technical Specifications

Parameter	Details
Material Type	Polymer matrix composite laminates
Specimen Type	Flat rectangular laminate with a centrally machined hole
Hole Diameter	Specified nominal size with tight machining tolerance
Specimen Width & Thickness	Defined by laminate configuration and standard requirements
Edge Distance	Minimum specified ratio of width to hole diameter
Tabbing	End tabs are bonded if required to prevent grip damage
Testing Machine	Calibrated Universal Testing Machine (UTM)
Loading Mode	Uniaxial tensile loading
Test Speed	Controlled crosshead rate as specified
Strain Measurement	Extensometer or strain gauges
Measured Parameter	Open-hole tensile strength
Environmental Conditions	Standard laboratory or specified temperature/humidity

Instrumentation Used for Testing

Universal Testing Machine (UTM)
Load Cell
Wedge or Hydraulic Grips
Extensometer (if required)
Strain Gauges (optional)
Drill/Machining Tool for Hole Preparation
Vernier Caliper / Micrometer
Data Acquisition System (DAQ)

Results and Deliverables

Open-Hole Tensile Strength
Maximum Load at Failure
Stress–Strain Data (if measured)
Failure Mode Classification
Specimen Dimensions and Hole Details
Test Conditions Documentation
Complete Test Report

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Frequently Asked Questions

ASTM D5766 determines the tensile strength of a composite laminate with a central hole drilled, testing the residual strength after damage due to stress concentration from fastener holes or penetrations.

Fastener holes in composites interrupt load-carrying fibers, resulting in stress concentrations. ASTM D5766 offers practical strength information for bolted joints, preventing premature failure of structures at joints subjected to loads.

ASTM D5766 is generally specified in the aerospace, automotive, wind energy, and defense industries where composite structures are typically loaded with high tensile loads and rely on mechanical fasteners.

The ASTM D5766 test method employs rectangular composite coupons that have a precision-drilled hole at their center. The hole geometry and edges must be accurately defined because the drilling quality affects the results of the open-hole tensile strength.

Unlike conventional tensile tests, the ASTM D5766 test method incorporates a controlled hole to introduce stress concentration, thus offering realistic strength information for composites that are used with mechanical fasteners or attachments.